Usually, a molded-case circuit breaker (MCCB) and an earth leakage circuit breaker are used in homes for prevention of fire or electric shock accidents. The molded-case circuit breaker (MCCB) is used for the purpose of protecting electric wires, and the earth leakage circuit breaker is used for the purpose of protecting a user by sensing an electric leakage on an electric circuit and shutting off electric power when the user gets shocked in the midst of using electric appliances.
Although molded-case circuit breaker (MCCB) and earth leakage circuit breakers have been widely installed in the world, a lot of fires break out every year worldwide. This is because arcing type fault occurs. Fox example, arcing type fault may occur due to aging of electric systems, insulation breakdown and wiring destruction, mechanical and electrical stress due to overuse or over-current, connection defect, or excessive mechanical damage to insulation and wiring in very various forms. This arcing type fault is low-current and high-impedance, and generates electric current that has an average RMS (Root Mean Square) value fewer than a thermal threshold of a circuit-breaker. Accordingly, the circuit breaker which is used as a cable cutting or interruption device does not react with a defective situation, and accordingly, fire may break out frequently.
Thus, an arc fault circuit interrupt (AFCI) device that can intercept electric arc fault is required compulsorily. Since 2002 in the U.S.A., an arc fault circuit interrupter (AFCI) has been required under many building codes.
As stated above, the conventional AFCI device has detected an amount of variation of the current that flows on a phase conductor line and a neutral conductor line to which alternating-current (AC) power source is supplied by a current transformer (CT), and judged whether the arc fault of an electric circuit occurs. When the arc fault of the electric circuit is generated, the electric power of the electric circuit is shut off.
However, since the conventional AFCI device is supplied with a direct power source from an AC line, there frequently occurs malfunction due to up-stream according to the input of an electric arc signal generated around the AC line. Also, an abnormal trip by lightening surges that flow in the AC line is generated to thereby cause the malfunction of the electric circuit.